Field of the Invention
Embodiments of the invention are generally directed to optical circuits; more particularly to electronic-photonic apparatus including, but not limited to, photonic integrated circuits; electronic-photonic integrated circuits (EPICs); optical pulse-train generators; a microring-based optical pulse-train generator; a time-interleaved optical pulse-train generator; an optical arbitrary waveform generator, associated methods, and applications.
Description of Related Art
Recent advances in silicon photonics have highlighted various electronic-photonic integrated circuits (EPICs) that can or soon will seamlessly integrate photonic devices with ultrafast electronics. Microring-based devices such as add-drop filters and modulators exhibit good optical performance with ultracompact device size, especially in high index contrast systems like silicon-on-insulator (SOI) technologies, hence potentially enabling very large scale EPICs. For example, Q. Xu et al., “Silicon microring resonators with 1.5-μm radius,” Opt. Express 16, 4309-4315 (2008) have demonstrated silicon microrings with 1.5 μm radii; others have proposed that millions of these devices can be used in an on-chip optical interconnect system.
Research efforts to date have focused on the filtering characteristics of microring circuits in the wavelength domain and their applications in wavelength-division multiplexing. For example, Little et al., “Microring resonator channel dropping filters,” J. Lightwave Technol. 15, 998-1005 (1997) derived the time-dependent transfer functions of a microring resonator with the basic add-drop configuration, treating the ring only as a filter in the wavelength domain. Time-domain properties of microring-based devices and their circuit applications have not been sufficiently explored, which can open up various important applications, e.g., microring-based optical delay lines with large group delays in an extremely small footprint as reported by F. Xia et al., “Ultracompact optical buffers on a silicon chip,” Nat Photon 1, 65-71 (2007). The inventors have thus recognized the advantages and benefits obtainable by exploring the time-domain applications of microrings on the circuit level, and the problem solutions these investigations would provide.
Further advantages, benefits, and solutions will be available by addressing the fundamental challenge in EPIC; i.e., the large potential bandwidth of photonics vs. the significantly lower speed of electronics. o overcome this mismatch, wavelength-division multiplexing can be used to split the large optical bandwidth in the wavelength domain. Another approach is to time-share the optical bandwidth by applying a time interleaving technique. Time interleaving has been widely used in the high-speed electronic circuits, such as analog-to-digital converters (ADCs), increasing the overall sampling rate by operating two or more data converters in parallel. Recently, time interleaving has also been introduced to EPICs, e.g., the photonic-assisted interleaved ADC as reported by G. C. Valley, “Photonic analog-to-digital converters,” Opt. Express 15, 1955-1982 (2007).
The inventors have thus recognized the advantages and benefits, and solutions that will be available by utilizing time interleaving techniques directly in the optical domain. Microring-based devices such as add-drop filters and modulators exhibit good optical performance with ultracompact device size, especially in high index contrast systems like silicon-on-insulator (SOI) technologies, hence potentially enabling very large scale EPICs. Therefore, using microring resonators as couplers to implement an optical pulse-train generator would result in an ultra-compact device compared to conventional technology. Such an optical pulse-train generator, e.g., could be applied to ultrafast optical arbitrary waveform generation. Unlike the conventional spatial approach of arbitrary waveform generation, such as chirp filters, frequency-to-space mapping or time-to-space mapping together with spatial modulation, a time-domain approach as proposed herein below could advantageously be utilized in high-speed instrumentation or applied in ultrahigh data rate optical communication at. Furthermore, our time-domain approach is more intuitive, easy to control, and allows more flexibility in output waveform generation.